1. Field of the Invention
The present invention relates generally to an integrated circuit (IC) package for enclosing an IC and, more particularly, to an IC package having a secure chip carrier for cryogenic cooling of the IC chip.
2. Art Background
Techniques for using cryogenic coolants such as liquid helium for reducing the operating temperature of an integrated circuit (IC) are well known in the prior art. One method for cryogenic cooling requires the use of a cold probe having a length of thermally conductive material. The cold probe includes a base end that is connected to a cryogenic cooling plant within which a cryogenic coolant is disposed and circulated. The cold probe also includes a contact end which is typically connected directly to the die of the IC via a tight thermal joint. As the base end of the cold probe is in direct contact with the cryogenic coolant, the temperatures of the cold probe and the die are reduced to approximately the temperature of the cryogenic coolant. Cryogenic cooling typically enhances the performance of the cooled IC.
FIG. 1 shows a typical prior art IC package design in which an IC 101 is epoxied to the substrate 103 of the IC package 100. Bond wires 102 are coupled between the IC and conductors disposed in the substrate 103. These conductors lead to the I/O pins 105. Lid 104 covers the cavity in which the IC 101 is placed. The flow arrows 106 illustrate thermal paths from the IC 101. The flow arrows 106 are shown to be directed from the IC package 100 and flowing to the ambient air outside of the package 100. This happens, for example, when the operating temperature of the IC 101 is greater than the ambient temperature of the atmosphere outside of the IC package 100. When the operating temperature of the IC 101 is greater than the ambient temperature of the air, it is desirable to have as many thermal paths away from the IC 101 as possible such that sufficient heat transfer may take place.
For cryogenic cooling of the IC 101, the package design of the IC package 100 is typically not altered in any substantial way. For example, the cold probe is often connected to the top surface of the die of IC 101, wherein the bottom surface of the IC 101 remains connected to the substrate 103. Unfortunately, the thermal paths through the IC package 100 become a liability during cooling because the direction of heat transfer reverses, and, unless the thermal load of the IC 101 is isolated from the ambient air, the cryogenic cooling plant will be forced to cool the ambient air.
The prior art discloses that an efficient method for isolating the IC 101 from the ambient air is to create a vacuum between the IC 101 and the ambient air. However, a typical prior art method for creating a vacuum requires surrounding the entire IC package 100 with an evacuated chamber. This solution requires a large amount of board space in a computer system and may significantly increase the footprint of the system. A further disadvantage of the prior art method is that permanent attachment of the cold probe to the die of the IC results in waste if either of the cold probe and the IC fails while the other continues to be operable.
As will be described, the present application discloses an integrated circuit package having a reduced number of thermal paths to an integrated circuit during the cryogenic cooling of the integrated circuit. The integrated circuit package of the present invention achieves isolation of the integrated circuit by creating a vacuum within the integrated circuit package itself.